This invention relates to an improved cutting assembly in the form of a rotary head for a rotary lawn mower, edger, trimmer or the like. The preferred embodiments are in the form of portable hand-held type lawn mowing and edging tools wherein the cutting element is safe in most uses and avoids the hazardous conditions created by prior art devices.
The prior art is prolix with attempts at solutions to provide a safe, efficient and simply constructed rotary head for rotary lawn mowers, edgers, trimmers and the like. Heretofore, the rotary head, or cutting blade, of rotary lawn mowers, edgers and the like have comprised a rotating metal bar or the like which is rotated at sufficient speeds to effect cutting of grass, weeds or the like. However, such bars create hazardous conditions in that when they strike certain objects they act upon those objects in a fashion to create and project dangerous missiles which may strike the operator or individuals in the area of work.
Various attempts have been made to overcome the aforesaid hazardous conditions created with rigid type metal cutting blades of the prior art. Most of these attempts to overcome the problem involve the utilization of some type of flexible flail which will have sufficient resiliency so as not to propel objects which are struck at high velocities. Most of these resilient type cutting elements of the prior art suffer a disadvantage in that they are not safe and mere resiliency is not sufficient to insure that the dangerous conditions will not be created when rotation is effected at desired cutting speeds. Further, the prior art cutting elements are generally not provided with means for easy replaceability in the event of wearing out and are usually expensive to replace.
The result has been that most of the prior lawn edging apparatus have been unsatisfactory because of the dangerous conditions created by the rotating head. As a consequence, most lawn edging and trimming around trees and the like, which would otherwise be damaged by the metal blades, must be done manually, which is both laborious and time consuming.
There is depicted and described in the following West German petty patents No. 6,919,841, No. 6,919,842, No. 6,919,843, No. 6,919,844, No. 6,938,265 and No. 7,043,648 one or more embodiments of a lawn mowing or trimming device having a disc-like head member arranged to be rotated by an electric motor, and containing a spool which is housed therein a coaxial relationship to the shaft of the motor. A length of flexible non-metallic line is coiled about the spool, whereby its free travelling end extends generally peripherally from the spool and head, and whereby such free travelling end will be swung arcuately about upon actuation of the motor to cut adjacent vegetation in the manner of a flail.
Use of the German device has revealed that, under ideal operating conditions, it will cut or trim grass and other light-weight vegetation with reasonable effectiveness. Furthermore, it possesses the significant advantage that it is much safer to use than the more conventional cutters, in that it does not cause stones or other solid objects to be discharged in the same dangerous manner, and it is almost completely incapable of causing any significant injury to persons or pets struck by the flailing cutting string. In fact, it is a reasonable statement that the German device will actually cut substantially only the vegetation to which it is directed.
On the other hand, the German device is also subject to certain disadvantages of a magnitude such as to severely limit if not destroy its practical value. In the first place, it is largely effective to cut standing light-weight vegetation but is almost completely useless for any other task. In the second place, it will only cut such vegetation if growing relatively sparsely, and it cannot effectively handle even light-weight vegetation if encountered in a rank condition. A more serious disadvantage, however, is that in the German device the cutting string experiences a breakage rate which is so high as to nullify all of its advantages and to keep such a device from having much commercial value.
It will be readily apparent from a consideration of the teachings hereinafter provided that a cutting string which is free from internal flaws or other defects will not usually break except as a result of being struck against or across a relatively immovable object. The cutting string may, of course, be formed of a metal wire or heavy strap in order to provide it with a tensile strength sufficient to resist such impact, but such a string will create substantially the same dangerous conditions which exist when the cutting element is a rigid blade or the like. Thus, the safety advantages which are present with the German device are directly derived from the same design feature which is the reason for excessive string breakage, i.e., the fact that the cutter used by the German device is a light-weight plastic string having a relatively small diameter, and therefore having a relatively poor tensile strength.
These disadvantages of the prior art, and especially the aforementioned German device, are overcome with the present invention, and commercially acceptable embodiments of a vegetation cutter and the like are herein provided which are not only fully capable of cutting vegetation under most operating conditions, but which are also fully capable of other tasks completely beyond the capabilities of the German device, such as cleaning dead leaves, trash and other such debris from along fences, walls and the trunks or stems of trees and bushes. More paticularly, however, the embodiments of the present invention are capable of operation with a much lower breakage rate for their cutting strings, without any sacrifice whatsoever of the safety features and advantages hereinbefore accorded to the aforementioned German cutting device.